tidyprompt 0.3.0

• llm_provider-class: can now take a stream_callback function, which
  can be used to intercept streamed tokens as they arrive from the LLM provider.
  This may be used to build custom streaming behavior, for instance to show a live
  response in a Shiny app (see new vignette("streaming_shiny_ipc") for an example)

• llm_provider_ellmer(): now supports streaming responses

• add_image(): new prompt wrap to add an image to a prompt, for use
  with multimodal LLMs

• answer_using_r(): fixed error with unsafe conversion of resulting object
  to character